Circuits for repeating square shaped wave forms



Now-2, 1948. I w. F. GLOVER I 2,452,563

CIRCUITS FOR REPEATING SQUARE .SHAPED WAVE FORMS Filed Jan. 11, 1945 F/Gl Inventor Patented Nov. 2, 1943 CIRCUITS FOR REPEATI'NG SQUARE SHAPED WAVE FORMS William Frank Glover, London, England, assignor to Standard Telephones and Cables Limited, London, England, aBritish company Application January 11, 1945,-Serial N0. 572,3 7 8 .lnzGreat Britain January 15, 1944 2 ihaimsl The present invention relates to an electric pulserepeating circuit containing a pulse transformer and concerns particularly an arrangement for applying magnetic bias to the transformer inorder to increase the amplitude of the pulses obtainable therefrom,

It is well known that the magnetic saturation of the core ofa transformer practically limits the amplitude of the output pulses. If the core is initially unbiassed, the maximum possible amplitude of theoutput pulse is substantially determined by the saturation value of the flux of the core. 'When the pulses are unidirectional, the core may be biassed practically to saturation in the negativedirection and then if the input pulse be applied so as to change the flux in the positive direction, the total flux change availablefor the production of the output pulse will now'be twice the saturation flux.

The present invention comprises a thermionic valve amplifier for pulses including a transformer from which the output pulses are obtained, and in which the transformer is magnetically biassed by a current derived from an electrode of one of the amplifying valves, so that a biassing flux is produced in opposition to the flux produced by the pulses.

' The invention will be described with reference to the accompanying drawing in which:

Fig. 1 shows a schematic circuit diagram of an embodiment; and

Fig. 2 shows a hysteresis curve used to explain the operation of the circuit of Fig. 1.

Referring to Fig. 1, there is shown a pulse amplifier comprising two valves VI and V2 shown for example as triodes, though any suitable valves having additional eletrocles may also be used. Unidirectional pulses are applied to the valve VI at the terminals IN through a blocking condenser Ci with such polarity as to drive the control grid negative. The anode of V! is coupled to the control grid of V2 through a b1ocking condenser 02 and resistance Bi and the output pulses are obtained from a transformer T with a core of iron or other magnetic material having its primary winding I, 2 connected in series with the cathode of V2, and its output secondary winding 3, t connected to a load represented by the resistance R2. GI and G2 are grid leak resistances for the valves Vi, and V2 respectively, and Al and A2 are appropriate anode series resistances. Cathode bias for the valve Vi is provided by the resistance R3 shunted by the condenser C3 and for the valve V2 by the resistance R4 shunted by the condenser C4.

A bias winding .15 (inf the transformer"?! is connected in series-with R3 so that it will be traversed by the steady cathode current of the valve Vi. The terminals .of the transformer windings are numbered in such ,a manner that the flux produced by --a currentwwhich flows from an odd numbered terminal to-an vevennumbered terminal is in the same direction for all the windings.

The action of .the transformer will .be vexplained with reference toFig. 2 which shows a typical hysteresis curve fora transformer'core. Assuming that no pulses. are applied tothe valve Vi, and that the winding 5, 5 is first disconnected, then the cathode current of valve V2 flowing through the winding .l, .2 will ,be supposed to produce a small magnetic fieldjn the core givenby the lengthpOS. The ,windingt, B being now re-connected, a superposed magnetic fi d in t e opp s t direction is produ ed y the cathode current of VI. "This opposing magnetic field is much larger and is represented by SN. The core is thus brought to the condition represented by the point P, the corresponding flux being represented by PN.

Now assume that a pulse is applied to the control grid of Vi in the negative direction, and of sufficient amplitude to reduce the cathode current to zero. At the same time a positive pulse is obtained at the anode of VI and this will be applied to the control grid of V2, increasing the cathode current which flows through the winding 5, 2 of the transformer. The magnetic field due to the cathode current of VI is substantially unaltered because of the large by-pass condenser C3 through which the pulse passes, but the field due to the cathode current of V2 alone increases from OS to Oh. The point L is beyond the saturation point of the core, but the presence of the biassing field SN effectively shifts the point L to M. The actual field change is such as to shift the point N over to M, and the operating point travels along the branch PTQ of the curve, the flux changing from PN to QM. A positive pulse will thus be obtained in the load R2 whose amplitude is proportional to 2 PN, if ON=OM. When the pulse disappears, the operating point returns to P over the branch QUP.

The positions of the points S and M can be selected by suitably choosing the number of turns of the winding l, 2 and the bias of the valve V2. Then the desired opposing field SN can be obtained by suitably choosing the number of turns of the winding 5, 6.

The transformer may be connected in various other ways besides that shown. For example, the bias current may be obtained from the anode circuit of valve VI and/or the winding I, 2 may be connected in the anode circuit of V2; or the bias winding could be energised for some other stage (not shown) of the amplifier, or by a screen grid current, for example.

Whatever arrangement is used for biassing the transformer, the bias flux produced by the current in the bias winding should be in the opposite direction to the change in fiux produced by the leading edges of the pulses in the primary winding.

Referring again to Fig. 2, the points S, M and N can generally be placed anywhere along the magnetic field axis. This permits a wide choice of 'so that the loading of the transformer will be only slightly, increased by the connection to the cathode circuit of Vi. Thus in a particular case of Fig. 1, z-

the cathode currents of the valves VI and V2 were 100 milliamperes and 6 milliamperes, respectively, and the turns ratio of the windings I, 2

' and 5, 6 was 10:1,

The chief advantage of the; arrangement of the invention is that the magnetic bias is obtained without any extra components and without any additional power supplies.

What is claimed is:

1. An amplifier for electric pulses comprising two thermionic valves, an output transformer having primary, secondary and biassing windings on a core of magnetic material, means to connect the primary winding to the output of one of the said valves, and means to supply current to an electrode of the other valve through the said biassing winding in such a manner as to generate in the said core a flux in opposition to the fiux produced therein by pulses transmitted through the said transformer.

2. An amplifier for electric pulses comprising input and output thermionic valves connected in tandem, an output transformer having primary, secondary, and biassing windings on a core of magnetic material, means to apply pulses to the control grid of the input valve, means to connect the said primary winding in series with the cathode of the output valve in such manner as to permit amplified pulses to be derived from the said secondary winding, and means to pass the steady cathode current of the input valve through the said biassing winding in such a manner that the fiux produced in the said core produced by pulses transmitted through the transformer is in opposition to the flux produced by the said steady cathode current.

WILLIAM FRANK GLOVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,808,726 Donle June 2, 1931 1,895,111 Suydam Jan. 24, 1933 46 2,417,296 Dikstaal Mar. 11, 1947 

